The purpose of the proposed research is to compare structurally several proteins observed in immunoprecipitates of SV40 infected cells. The proteins include two known products of the SV40 early genes, proteins with molecular weights of 94,000 and 17,000 daltons. Two additional proteins with molecullr weights of 56,000 and 32,000 daltons are also present in cells infected with wild-type virus, but are absent from immunoprecipitates of cells infected with certain non-transforming deletion mutants. The possibility that the 56K and 32K proteins are only observed when complexed to the 17K viral gene product is being explored.